“We’re sick of it,” she said. “All this stuff that they’re saying, it sounds like a junior-high-school campaign.”

A Democrat who caucused for President Obama in 2008, Stehn, 57, attended his campaign rally Wednesday by the banks of the Mississippi River and is enthusiastic about voting for him again. She reserves most of her disdain for what she says are Republican challenger Mitt Romney’s “lies and distortions.”

But she’s also disappointed that Obama chose to engage: He slyly joked in Iowa this week about the infamous incident when Romney drove to Canada on vacation with the family dog in a carrier on the roof of the car.

The Romney campaign, meanwhile, offered its own blasts, suggesting that Obama should take his “campaign of division and anger and hate back to Chicago.”

From incendiary rhetoric, such as that Romney’s plans for Wall Street would put people “in chains,” to saying that Obama’s campaign “has disgraced the presidency,” campaign 2012 is knocking on the door of being the ugliest in a generation, and the party conventions haven’t even been held yet. It’s unfolding amid claims from both sides that the race will be about substance and big issues.

Given the stakes, that’s unlikely to happen. The latest round of fighting “reinforces the view of a lot of people” that politicians too often are squabbling and not doing what they were elected to do, said Dennis Goldford, a professor of politics at Drake University in Des Moines, Iowa.

A Gallup survey last month found that 64 percent were thinking quite a lot about the election. But that’s down from comparable 2004 and 2008 levels, Gallup said, and turnout could suffer. Indeed, one big risk with ratcheting up the rhetoric, experts say, is that the already-alienated segment of the electorate will find fresh reasons to stay home on Election Day. A new Suffolk University-USA Today poll released Wednesday found that about 40 percent of adult Americans don’t plan to vote this fall.

The main reason? People were too busy, or thought their votes didn’t matter. And majorities said they didn’t pay attention to politics because it was corrupt and a bunch of empty promises.

Both campaigns might want to think about the fallout of their messaging lately. Stehn said she feared the president’s remarks on the dog controversy could turn off independents. Crowds laughed, but Stehn said, “if you’re a supporter, you roll your eyes and wish he’d stop doing it.”

Harry Tibbetts, 72, an Obama supporter in Dubuque, said the two candidates “are telling outright lies about each other, especially that Romney guy.”

Still, Obama has “got to come back at him,” the retired Reliant Energy worker said. “You fight fire with fire.”

All signs point to more of the same.

“This campaign is going to set the standard as the most despicable since 1988, and this year it’s both sides who are doing it,” said Tobe Berkovitz, a former Boston-based Democratic media consultant who now teaches communications at Boston University.

That was the year President George H.W. Bush’s campaign ripped into Massachusetts Gov. Michael Dukakis, the Democratic nominee, for furloughing Willie Horton, a black inmate who terrorized a white Maryland couple while out of jail. The Bush forces had an ad suggesting a Dukakis presidency might mean that more Hortons would be free.

The rhetoric this year is approaching that level.

This month, Senate Majority Leader Harry Reid, D-Nevada, claimed on the Senate floor that Romney had paid no taxes for 10 years, but Reid has offered no solid proof.

An ad by a group that backs Obama tried to link the death of a steelworker’s wife to Romney’s tenure at Bain Capital, the investment firm he co-founded. But the steelworker lost his job at the Bain-purchased Kansas City steel plant after Romney left Bain, and his wife didn’t become sick until several years later. Romney ran an ad calling the charge “disgusting.”

Language criticized

The latest bout began Tuesday, when Vice President Joseph Biden told a Virginia audience that included hundreds of African Americans that Romney “is going to let the big banks once again write their own rules. Unchain Wall Street,” he said, adding, “He is going to put y’all back in chains.”

Romney has said he wants to revamp certain regulations that affect banks and investment firms to make them more realistic.

Romney fired back, accusing the Obama administration of fostering “division and anger and hate.” Obama’s allies suggested Romney had become “unhinged.” Then Romney said Wednesday morning on CBS that Obama “seems to be running just to hang on to power. I think he’ll do anything in his power to try and get re-elected.”

Republicans said Biden’s remarks carried racial overtones and demanded that Obama condemn them. In an interview with People magazine Wednesday, Obama defended Biden, saying his running mate’s only meaning was that consumers won’t be protected if Wall Street reforms are repealed.

“In no sense was he trying to connote something other than that,” Obama said.

Former Virginia Gov. L. Douglas Wilder, a Democrat and the nation’s first elected black governor, lambasted Biden for the comments. On CNN, Wilder called on the vice president to “cool it, back up” and admit he was wrong.

It’s unclear whether Romney can convince voters that Obama is a politician of volcanic anger and ambition. Sometimes called “no-drama Obama,” the president has disappointed liberal activists who see him as too dispassionate, meek and willing to compromise on issues such as a government-provided health insurance option.

Some GOP activists say Romney’s time would be better spent talking about jobs and the economy, even if Obama has pitted wealthy Americans against the less-wealthy and allowed allies to level harsh charges against Romney.

“He is the most divisive president ever,” said Virginia-based GOP consultant Mike McKenna. “But he doesn’t seem angry, which is why he retains his personal popularity.”

Summertime demonizing is not new. In 1996, President Clinton was able to define Republican challenger Bob Dole as closely tied to congressional Republicans who were falling out of public favor. Backers of President George W. Bush raised questions in 2004 about the Vietnam War service of Massachusetts Sen. John Kerry, the Democratic standard-bearer and a decorated veteran.

What’s different is that the rough-and-tumble of the race has come earlier and is harsher, with both sides playing to their bases of support. The undecided vote is seen as roughly 10 percent of the electorate, according to polling.

Said David Carney, a GOP political consultant: “It’s much easier to turn out 80 to 85 percent of your base than to convince the undecided.”